The present invention relates generally to a clutch device, and more particularly, to a clutch device having clutch disk cushioning means such that during engagement and disengagement of the clutch the biasing of the clutch pressure plate combined with the cushioning means provides a force displacement response of the pressure plate that is at least partially nearly linear. The clutch device further Includes a torque limiter for reducing the adverse effects of the use of the engine as a brake.
Motorcycles are typically provided with a clutch device for selectively transmitting rotary power between the crankshaft of an internal combustion engine mounted to the motorcycle frame and the input shaft of a transmission also mounted to the motorcycle frame. Such clutch devices are generally mounted proximate the input shaft of the transmission. Power Is transmitted to an input part of the clutch device through a gear train from the crankshaft of the engine, and is transmitted to the input shaft of the transmission through a clutch body and a clutch output part.
Some clutch devices used oil motorcycles are of a multiple disc type in which a plurality of clutch plates are disposed side by side within the clutch assembly. In such a clutch assembly, there are usually at least two clutch plates. One plate is coupled to rotate with the crankshaft of the engine and one plate is coupled to rotate with the input shaft of the transmission. A pressure plate within the clutch device, usually spring biased, selectively exerts a compressive force against the plates so that they rotate together to transmit rotary power therebetween. The pressure plate is usually connected to a release mechanism such as a lever on the handlebar of the motorcycle. The pressure plate is engaged and disengaged via movement of the lever. The clutch is engaged to transmit rotary power when the plurality of clutch plates are compressed by the pressure plate, and are disengaged when the pressure plate is moved against the force of the spring biasing so that the clutch plates may rotate independent of each other.
In the above described conventional clutch device, a plurality of coil springs are used so as to bias the pressure plate. To effect disengagement of the clutch, the pressure plate is moved against an urging force of the coil spring using the release mechanism. As the pressure plate is moved to disengage the clutch, the coil springs are compressed. The load characteristics of the coil springs are typically linearly sloped, such that, as the springs are compressed, a linearly increasing force must be exerted against the springs to further compress the springs. As a consequence, the force exerted by a motorcyclist via the handlebar lever must gradually increase as the clutch releasing operation progresses. It Is therefore often difficult for motorcyclists to smoothly perform the clutch engaging and disengaging operations. Often, when such clutches are engaged, the motorcyclist will experience a jolt or a shock if the clutch engages too quickly, i.e if the clutch lever on the handlebar is released to quickly.
Some industrial clutch devices are equipped with a cushion spring which opposes the biasing of the coil springs in order to alleviate the shock experienced when the clutch is engaged. The purpose of such a cushion spring is to protect expensive equipment. In such an industrial clutch, when the cushioning properties of the cushion spring and the load characteristics of the coil spring are combined with each other, the release load characteristics become parabolic rather than linearly sloped (i.e. the response experienced upon movement of the clutch engagement mechanism becomes parabolic). The release load characteristics are such that the force necessary to release the clutch (i.e. to move the pressure plate) rapidly increases as the releasing operation is performed, thereby making It difficult to smoothly perform the releasing operation.
The rotary power provided by an engine is normally used to move a vehicle. However, it is also possible to use the torque of an engine to stop or slow a vehicle down by engaging the clutch when the transmission input shaft is rotating at a faster speed than the crankshaft of the engine. When the slower rotary torque of an engine is used to slow a vehicle down, is referred to as an engine brake. In automotive applications, use of the engine as a brake is common practice. However in a motorcycle, engine braking can be dangerous. If the engine brake is applied too rapidly, the rear motorcycle tire may, in some cases, slip. Tire slippage may cause the motorcyclist to lose control of the motorcycle. The results can be disastrous.